1. Field of the Invention
The present invention relates to a piezoelectric/electrostrictive device having a light modulation mechanism for use in an image display unit, an image printing unit, an exposure unit, an optical switch, or a like apparatus.
2. Description of the Related Art
Recently, various devices having light modulation mechanisms have been developed. For example, Japanese Patent Application Laid-Open (kokai) No. 5-196880 discloses a deformable mirror device (hereinafter called a DMD). As shown in the schematic perspective view of FIG. 33, the DMD includes a CMOS substrate 200; two support elements 202 disposed on the substrate 200; a pair of torsion hinges 204 supported by the support elements 202; a yoke 206 supported by the support elements 202 via the torsion hinges 204; and a mirror 208 supported by the yoke 206. The torsion hinges 204 are twisted through utilization of electrostatic attraction, to thereby change the angle of the mirror 208. For easy understanding, the mirror 208 in FIG. 33 is represented as being transparent.
The DMD is said to enable reduction in device size and highly dense arrangement of pixels. However, since the torsion hinges 204 are twisted so as to drive the mirror 208, the torsion hinges 204 tend to suffer fatigue. Also, since electrostatic attraction is utilized for driving the mirror 208, the mirror 208 may be stuck during operation.
As shown in the schematic sectional view of FIG. 34, a thin-film actuated mirror array (hereinafter called AMA) disclosed in Japanese Patent Application Laid-Open (kokai) No. 11-72724 includes an actuating portion 312 supported by an anchor 302 formed on a substrate 300. The actuating portion 312 consists of a support layer 304 supported by the anchor 302, a bottom electrode 306 formed on the support layer 304, a deformable layer 308 containing a piezoelectric substance and formed on the bottom electrode 306, and a top electrode 310 formed on the deformable layer 308. A stress balance layer 316 is supported on the actuating portion 312 via the post 314, and a light-reflecting member 318 is formed on the stress balance layer 316. Voltage is applied between the bottom electrode 306 and the top electrode 310 so as to deform the deformable layer 308. Through deformation of the deformable layer 308, the actuating portion 312 is inclined, to thereby incline the light-reflecting member 318. For changing the angle of the light-reflecting member 318 the AMA utilizes deformation of the deformable layer 308 containing a piezoelectric material instead of torsional movement of a torsion hinge. As a result, a drive part is less likely to suffer fatigue. Also, since the AMA does not employ electrostatic attraction, the light-reflecting member 318 is unlikely to become stuck.
However, the AMA involves the following drawbacks. Since the light-reflecting member 318 is formed in parallel with the deformable layer 308, the length of the deformable layer 308 must be increased when a large deflection angle (the angle of tilt of reflective surface) is required. As a result, the size of the element increases. Also, since the light-reflecting member 318 is formed of a thin metal film, whose rigidity is low, the reflective surface implemented by the light-reflecting member 318 encounters difficulty in maintaining flatness. Since the flatness of the reflective surface changes with time as a result of operation of the AMA, the operation of deflecting the reflective surface cannot be performed stably over a long period of time.